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Old 02-22-2018, 08:05 AM   #1
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Alloy analysis

I’ve been curious about the actual alloy(s) used by Airstream over the years, particularly regarding the formed endcaps. We all ‘know’ that the vintage outside skins are 2024 Alclad because they can be polished. But what about the stretch formed endcaps? From what I have found, 2024T3 can’t be formed, plus we all know they are ‘soft’. It’s easy to question this, a friends polished late ‘70’s trailer has a visual difference from the sides to the endcaps. Is it 2024-T0, stretched and work hardened or a different alloy?

It doesn’t take much digging to find the attached Alloy.pdf that summarizes some of the materials and timeframe but it never addressed the endcap question.

I had the chance to use an X-ray fluorescence meter and scan 7 different skins/endcaps and the results had some surprises.

I started with a stock piece of 2024-T3 Alclad. The scan showed below spec Copper (Cu) content caused by the pure aluminum coating. It still is recognizable as 2024 alloy.

1955 parts, scanned on the back side (non-Alclad according to documentation?) matched 2024’s spec’s. No stretched parts in this vintage. They are inked on the backside showing the 24 S T 3 alloy
1961 skins AND endcaps are 2024. Looks like they used 2024-T0 and let it work harden during the forming.
1963 was a surprise, it’s not 2024 alloy. It shows as a high zinc 5000 series for end caps and skins. Both a California and Ohio trailer gave the same results.
1975 Ohio Trailer has 2024 sides but the same high zinc 5000 series endcaps as the ’63 trailers.
1991 metals are documented as 3005 and they do scan as a 3000 series, endcaps and sides.
2005 metals also scan as a 3000 series but with lower Cu than the 1991 alloy.

I answered my question, the old stuff has the same alloy on the caps as the skins (but it may not be 2024!). The ’75 trailer has different caps than skins. The later trailers use some derivation of the 3000 series alloys. The surprise was the false assumption that up thru the 70’s everything was 2024 Alclad because both ‘63’ trailers don’t have anywhere near enough Cu to qualify as a 2XXX alloy.
I've attached the data that was generated.
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Old 02-22-2018, 12:18 PM   #2
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Your XRF was giving quantitative results? We use PIXE at our lab and it is not the best for getting material ratios, I thought XRF was worse because of the background noise? Must be new detectors are better than the old SiLi type.
I would try PIXE, but you have to fit the vehicle on our freight elevator to our nuclear accelerator ;0
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Old 02-22-2018, 12:32 PM   #3
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Quote:
Originally Posted by WayneG View Post
...you have to fit the vehicle on our freight elevator to our nuclear accelerator ;0
LOL. That's the reason I used a handheld XRF, I didn't feel like cutting 2"x2" chunks out of every Airstream I could find.

The handheld didn't have a protocol for true identification so I ran it in one of the Mine modes. It got the basic metals except for Magnesium and the actual Aluminum, that was enough to place it into one of the alloy families.

I was really hoping that the unit would just catch the surface elements and let me know if the panels were Clad but it actually penetrated into the sheet and I.D.'d the alloy'd metals.
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Old 02-22-2018, 02:01 PM   #4
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Itís hard to believe the clad would skew the quantitative copper results that much. Is it possible the results are instrument error and normal variance in alloy composition?
Or maybe Airstream was buying aircraft alloy that was slightly below spec that was rejected by Boeing or Northrop or McDonnell Douglas.
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Old 02-23-2018, 04:24 PM   #5
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Quote:
Originally Posted by markdoane View Post
Itís hard to believe the clad would skew the quantitative copper results that much. Is it possible the results are instrument error and normal variance in alloy composition?
Or maybe Airstream was buying aircraft alloy that was slightly below spec that was rejected by Boeing or Northrop or McDonnell Douglas.


Since my 1st objective was to see if the formed endcaps were really clad and that didn't work out, I was pleased that the data could at least indicate the class by looking at the main alloy material.

I can't find a definitive answer to how deep the scan goes into the sheet metal. It's obviously making it thru the alclad and picking up the base alloy. I do know the system assumes a homogenous material so a layer of pure aluminum over the alloy will skew the results. In other words, if the clad was thick enough, the results would show 100% aluminum. I just can't find any info on how thick it would need to be for this type of result.
Supposedly Airstream swapped vendors in the early '60's, that must be the difference between the '61 trailer and the '63's. Unlike an Aircraft manufacturer, I doubt Airstream required material certifications so the final mix of metals, well let's say, could be subject to variation.

Plus it was fun messing around with a really expensive gadget...
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and a 26' '63 Overlander, Dolly http://www.airforums.com/forums/f109...ome-71609.html
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Old 02-24-2018, 04:17 AM   #6
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I can send a email to our XRF Guru Professor to see if he has any info on depth vs response. I never got into the details myself.
If you can get me some info on your detector and the settings you used that would help.
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Old 02-24-2018, 07:27 AM   #7
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Believe it or not, I helped a person with a trailer that was skinned on the driver's side with 7075-T6. Had to replace as it was so corroded. It was also the original skin.
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Old 03-01-2018, 08:01 AM   #8
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Quote:
Originally Posted by WayneG View Post
I can send a email to our XRF Guru Professor to see if he has any info on depth vs response. I never got into the details myself.
If you can get me some info on your detector and the settings you used that would help.
Wayne - here is the unit;

https://www.thermofisher.com/order/c...oduct/10131166

Quote:
Originally Posted by Aerowood View Post
Believe it or not, I helped a person with a trailer that was skinned on the driver's side with 7075-T6. Had to replace as it was so corroded. It was also the original skin.
Kinda confirms my suspicion that they used whatever was available, huh?
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and a 26' '63 Overlander, Dolly http://www.airforums.com/forums/f109...ome-71609.html
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Old 03-01-2018, 08:24 AM   #9
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Email sent, Hopefully he answers soon
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